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REVIEWOpenAccessMicelles,mixedmicelles,andapplicationsofpolyoxypropylene(PPO)-polyoxyethylene(PEO)-polyoxypropylene(PPO)triblockpolymersVijenderSingh1,2,PoonamKhullar2,PragneshNDave1*andNavjotKaur3AbstractThisreviewgivesabriefoutlineofvariousmicellarpropertiesoftriblockpolymerssuchascriticalmicellizationconcentration,criticalmicellizationtemperature,andmicroviscosity.
Detaileddiscussionoftheeffectoftemperatureonmicellarpropertiesofvarioustriblockpolymermixturesisgiven.
Applicationsoftriblockpolymersinsolubilizationasdrugdeliveryagents,asnanodrug,forthesynthesisofgoldnanoparticles,forcobaltdetermination,etc.
arediscussed.
Keywords:Micellization,Criticalmicelleconcentration,Cloudpoint,CriticalmicelletemperatureReviewCharacteristicfeaturesoftriblockpolymersTriblockpolymers(TBPs)alsoknownasblockcopolymersbelongtoaclassofnonionicsurfactants.
Theyarecom-merciallyavailableunderthetradenamesPluronics(BASF,Ludwigshafen,Germany),Poloxamers(ICI,London,England),orSynperonics(ICI)andarehighlysurface-activecompounds.
Theblockcopolymersconsistofalinearhydrophobicpolyoxypropylene(PPO)blockwithhydrophilicpolyoxyethylene(PEO)blocksoneachsidewiththestructurePEO-PPO-PEO.
Theirhydrophilic-lipophilicbalance(HLB)dependsonthePEO-to-PPOmassratio[1,2].
TherichpolymorphicbehaviorofPluronicsismodulatedbytheirHLB[3].
ThePEO-PPO-PEOTBPsarecommerciallyavailableinarangeofmolecularweightsandPPO-PEOcomposition[4].
Greateramountofoxy-ethylenegroups,forinstance,impliessignificantaqueoussolubility.
TBPsarethesubjectsoffundamentalaswellastechnologicalresearch[5-7]thatarisesfromtheirabilitytoformmicelles,macro-ormicroemulsions,andseveralliquidcrystallinephases[8-10].
Becauseoflowtoxicityandhighbiodegradability,thesecopolymershaveextensiveindustrialapplicationsindetergency,paintin-dustries[11],cosmetics,dispersionstabilization,foaming,lubrication[12,13],andpharmaceuticalformulation[14,15].
Otherimportantapplicationsincluderadiation-damagedcellrepairandtreatments,controlleddrugdelivery,bio-processing[16],nuclearwasteprocessing[17,18],foodprocessing,aswellasinagriculturalformulations[19-21].
Furtherapplicationsareemulsion[22]andstabilizationinpolymerizationreaction[23],nanomaterialsynthesis[24,25],andcoalprocessing[26].
Fundamentally,theyhavetremendousadvantagesthanconventionalneutralpolymersduetothepresenceofbothhydrophilic(i.
e.
,PEO)andhydrophobicpredominant(i.
e.
,PPO)moietiesinthesamepolymermolecule.
Inanalogywiththelowmolecularweightsurfactants[27],blockcopolymersformaggregatesofdifferentkinds,de-pendingonthemolecularweight,blocksizes,solventcomposition,andtemperature.
ThelowmolecularweightPluronicsareviscousoilsorpastes,andhighmolecularweightPluronicsareamorphoussolids.
Thedifferenttypesofblockswithinthecopolymerareusuallyincom-patiblewithoneanother,andasaconsequence,blockcopolymersself-assembleinmeltsandinsolutions.
Theyalsoshowanomalousbehavioroveracertainrangeoftemperature,aneffectshown,ingeneral,byblockcopoly-mersinselectivesolvents[28,29]whichhasbeenfoundduetothepresenceofmorehydrophobiccomponentpresentasimpurity[30,31].
*Correspondence:pragnesh7@yahoo.
com1DepartmentofChemistry,KSKVKachchhUniversity,Bhuj,Gujarat370001,IndiaFulllistofauthorinformationisavailableattheendofthearticle2013Singhetal.
;licenseeSpringer.
ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense(http://creativecommons.
org/licenses/by/2.
0),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.
Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12http://www.
industchem.
com/content/4/1/12MicellizationCriticalmicelleconcentrationTheparameterofgreatestfundamentalvalueisthecriticalmicellizationconcentration(CMC),thecopolymercon-centrationatwhichmicellesstartforming[32].
TBPsarethenonionicsurfactants,whichlimitthenumberoftechniquesavailabletomeasuretheCMCincompari-sontothoseofionicsurfactants.
Alsoincomparisonwithconventionallowmolecularweightsurfactants,thereissomeinherentcomplexityinthemicellizationofblockcopolymers,whichdependsstronglyontheircomposition[33-42].
Theblocksarenotcompletelymonodisperseevenforacopolymerwithanarrowdistributionofmolecularweight,andaccordingly,nosharpCMC/criticalmicelliza-tiontemperature(CMT)hasbeenobservedforblockcopolymers.
Generally,theCMCspansoveramuchlargerconcentrationintervalthanobservedwithconventionalsurfactants.
TheCMCisalsosensitivetothetemperaturewhichislikelytoextendtheconcentrationrangeoverwhichtheCMCoccurs[33].
Varioustechniquessuchaslightscattering[33,43],fluorescencespectroscopy[44,45],NMR[46],specificvolume[47,48],andsmall-angleneu-tronscattering(SANS)[49,50]havebeenfrequentlyusedtogainnewinsightintotheaggregationbehaviorofthesesystems.
Theprocessofself-associationcanbeinducedbyincreasingtheconcentrationofTBPsabovetheCMCandadjustingthetemperaturetoCMT[30,51-56].
MicellizationinTBPsisunderstoodtoariseduetothefollowingreasons[29,57].
Asthetemperatureofablockcopolymersolutionisraised,thePPOblockpro-gressivelylosesitshydrationsphere,resultingingreaterinteractionsbetweenthePPOblocks.
Ontheotherhand,thePEOblocksretaintheirstronginteractionwithwater;thusasiscommonforallamphiphilicmolecules,thedifferingphasepreferencesoftheblocksdrivethecopo-lymerstoformmicelles.
Structuralstudies[31,58-63]haveshownthatthemicellesformahydrophobiccoreconsistingmainlyofweaklyhydratedPPOblocks,whicharesurroundedbyanoutershellknownascoronaofalmostfullyhydratedPEOblocks(Figure1).
ThereisabroadtemperaturerangeabovetheCMTwherethemicellescoexistinasolutionwithunimers.
Abovethetransitionregion,mostoftheblockcopolymermoleculesformmicelles[64-71].
ThereasonthatahighertemperatureisneededtoformmicellesisthattheeffectivePEO-PEO,PPO-PPO,andPEO-PPOinteractionsaretemperature-dependent.
Atsometemperature,theeffectivePPO-PPOattractionwilldominateoverthePEO-PEOrepulsion,andmicelleswillform(Figure1).
CMTofsomecommontri-blockpolymerislistedinTable1.
Micelleformationisanextremelytemperature-dependententropy-drivenprocessresultinginalargedecreaseinCMCuponincreasingthetemperature.
ThisbehaviorhasledtothewideapplicabilityofCMTasaconvenientmicellarparameter.
AbovetheCMT,unimersandmicellesexistinthestateofequilibriumwithmostofthecopoly-mermoleculesinthemicellarform.
TheeffectsoftemperaturesonthepropertiesandstructureofthePEO-PPO-PEOcopolymersolutionhavebeenstudiedextensively[59,72].
Aninterestingpropertyoftheaqueousmicellarsystemisitsabilitytoenhancethesolubilityinwaterofotherwisewater-insolublehydrophobiccom-pounds.
Thisoccursbecausethecoreofthemicelleprovidesahydrophobicmicroenvironmentsuitableforsolubilizingsuchmolecules.
Manyofthesecopolymersassociateinaqueoussolu-tiontoformsphericalmicelles[8,59,73],whileathigherconcentration,blockcopolymerscanalsoself-assembleintolyotropicliquidcrystals[54,74,75].
TheprogressivegrowthofthehydrophobiccorewithincreasingtemperatureduetotheincreasingdehydrationofPEOblocksinthecoronainducesinstabilityinthesphericalmicellardisper-sion,leadingtotheformationofrod-likestructures.
Theadditionofmultivalentsaltstoaqueouscopolymersolu-tionsproducesadramaticeffectonthetransformationofPEOPEOPPOTriblockpolymerPPOPPOPPOPPOPPOPPOPPOPPOPPOPEOPEOPEOPEOPEOPEOPEOPEOPEOPEOPEOPEOPEOPEOPEOPEOPEOPEOPPOPEOPEOPPOPEOPEO[Triblockpolymer]TemperaturecmccmtmonomersmicellenmnFigure1Schematicrepresentationofthegeneralstructureoftriblockpolymerandmicelleformation.
Withrespecttotheincreaseintheconcentrationandtemperature.
Table1CMTdata0.
1%solutionofTBPsTBPsConcentration(mM)CMT(°C)L640.
34539.
5P650.
29446P840.
23837P850.
21737.
5F880.
08848.
5P1030.
20224.
5P1040.
16927.
5P1050.
15427F1080.
06836Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12Page2of18http://www.
industchem.
com/content/4/1/12thecopolymer[76].
Atlowconcentration,sphericalmicellesform,whereasathighconcentration,thefor-mationofhexagonal,cubic,andlamellarliquidcrystal-linephasestakesplace[58].
Themorphologyspectrumrunsfrommicelles(L1),throughacubicarrayofmicelles(I1),hexagonallypackedrods(H1),andcubicbicontinuousspheres(V1),tolamellae(L3)wherephaseinversiontakesplace,andtheinvertedmorphologiesdevelop:cubic(V2),reversedhexagonal(H2),cubic(I2),andreversedmicelle(L2)[77,78].
Regularmicellesareformedinpolarsolventssuchaswaterandalcohols;thus,thecoronahasahydrophiliccharacter.
Micellesformedinnonpolarsolventssuchastoluenehaveahydrophobiccoronaandarereferredtoas'reverse.
'Re-cently,muchattentionhasbeendevotedtohighlyasym-metricblockcopolymersthatformaggregatescharacterizedbyalargecoreandathincoronalshellofthesolubleblock:thecrew-cutsystems[79,80].
'Crew-cut'micelle-likeaggre-gatesrepresentanewtypeofaggregate.
Theyareformedviatheself-assemblyofahighlyasymmetricamphiphilicblockcopolymer,inwhichtheinsolublecore-formingblocksaremuchlongerthanthesolublecorona-formingblocks[81,82].
Oneofthenoteworthyphenomenaasso-ciatedwithcrew-cutaggregatesistheaccessibilityofawiderangeofmorphologies[79,81,83,84].
Theseincludespheres,rods,vesicles,lamellae,largecompoundmicelles,largecompoundvesicles,ahexagonallypackedhollowhoopstructure(the'HHH'structure)[85],onions[86],abowl-shapedstructure[87],andseveralothers[88,89].
CloudpointandmicroviscosityAnotherparameterofgreatpracticalimportanceofTBPsinaqueousphaseisthecloudpoint(CP)[73,90,91].
AthighertemperatureswellabovetheCMT,thecopolymersolutionbecomesopaquebecausethephaseseparationbetweenthepolymerandwateroccurs.
ThetemperatureatwhichcloudinessappearsduetotheprecipitationistheCPofTBPs[92,93].
TheCPphenomenoninTBPsisrelatedtothecoreandcoronamodeloftheTBPaggre-gates.
ThismodelsuggeststhatthecoreofTBPmicellesmainlyconsistsofPPOunitswhilethecoronaoccupiesPEOunits.
ThepresenceofetheroxygensbothinthePPOaswellasPEOunitsallowssomenumberofwatermoleculestobeevenavailableinthecore.
AnincreaseinthetemperaturethusdehydratestheTBPmicellesevenatoptimumtemperaturesbyexpellingwatermole-cules,whichareweaklyassociatedwithetheroxygensthroughtheelectrostaticinteractions.
AtCP,theattractiveinteractionsbetweenPEOblocksandwatermoleculesaresufficientlyweakthatthePEOblocksbecomecompletelydehydrated.
Ithasbeenobserved[94,95]thatanyfactorwhichwouldincreasethenumberofwatermoleculesinTBPmicelleswouldresultinanincreaseinCPandviceversa.
TheTBPscontainingalargerPPOblockthanthatofPEOhavehighermicroviscosity[96-98].
Themicro-viscosityisstronglyaffectedbythePPOblock.
Itappearsthatthelargeritsmolecularweight,themoreviscousthemicelleinterior.
Amongthetwodifferentpolymers,themicelleswithalargerPPOblockexhibithighermicrovis-coscity.
Cloudpointofsomecommontriblockpolymersolutionsof1%concentrationiscitedinTable2.
MixedmicellesLikeconventionalsurfactants,TBPsshowaclearmicelleformationprocesswhichcanbebestdemonstratedbythechangeinI1/I3pyreneratioversusconcentrationplots.
SincetheanterioroftheTBPmicelleisconsti-tutedbythepredominantlyhydrophobicPPOunitssur-roundedbyhydrophilicPEO,thereforepyrenecaneasilysolubilizeinthecoreofthemicelleandhencecanactasafineprobeforthemicelleformationprocess.
TheI1/I3ratioissensitivetothemicroenvironmentofpyrenesolubilization,andhence,itsvariationexplainsthemicelleformationprocess.
InaqueousTBPsolutions(Figure2),itusuallystartsfromapproximately1.
75(valueinpurewater)anddecreasestoaconstantvaluearound1.
3whereitissolubilizedintheTBPmicelle.
Simi-larmethodscanverywellbeadoptedforthemeasure-mentsofCMCforthemixedcomponentsoverthewholemolefractionrange.
P103+TBPsmixturesP103consistsof60POunitsincomparisonto34EOunits.
ItmakesthisTBPpredominantlynonpolar.
ThevariationofmixedCMCvaluesfordifferentmixturesofP103isshownin(Figure3)alongwiththeidealmixing.
ItisusuallydifficulttodeterminefromtheCMCprofileswhichmixtureshowsgreaterattractiveorrepulsiveTable2Cloudpointof1%solutionofTBPsTBPsCloudpoint(°C)L3573F38>100L4237L4342L4465L6232L6334P8474P8585F127>100P12390L12219L6458P10386Singhetal.
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8050100150cmcI1/I3[L64]/10-4-3(d)1.
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801020304050[P84]/10-4-3I1/I3(c)cmcmoldmmoldmmoldmmoldmFigure2CriticalmicelleconcentrationofdifferentTBPs.
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81cmc(P103+P84)cmc*P103(b)cmc/10-4moldm-30102030405000.
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81cmc(P103+L64)cmc*P103(c)cmc/10-4moldm-30.
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81cmc(P103+P123)cmc*P103cmc/10-4moldm-3(e)Figure3CriticalmicelleconcentrationversusmolefractionofP103.
For(a)P103+F127,(b)P103+P84,(c)P103+L64,(d)P103+P104,and(e)P103+P123binarymixtures,respectively.
Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12Page5of18http://www.
industchem.
com/content/4/1/12interactionsduetothecourseofmicellization;therefore,theregularsolutiontheorybasedontheidealmixingisthebestwaytoestablishthenon-idealbehaviorintermsofparameter'β.
'Theaverageofβvaluesoverdifferentmixingratiosforeachmixturehelpstounderstandthefactonhowonemixtureofintermolecularinteractionsisdifferentfromothermixtures.
Averageβvaluesplot-tedagainstthePPO/PEOratiofordifferentmixturesareshownin(Figure4).
Apositiveandnegativevaluerespectivelyindicatestheoperatingrepulsiveandattract-iveinteractionsbetweenthecomponentsofthemixtures.
βAvgbecomesmorenegativeasPPO/PEOincreasesandapproaches1.
5.
FurtherincreaseinthePPO/PEOratioin-stantaneouslyconvertsβAvgfromanegativetoapositivevalue.
ComponentswithlowerPPO/PEOratio(i.
e.
,F127,P84,andL64)showattractiveinteractionswithP103,whilethecomponentwithgreaterPPO/PEOratio(i.
e.
,P104andP123)showsunfavorablemixingwithP103whichisclearlyrelatedtothedelicatebalancebetweenthePOandEOunitsinamixedstate.
P103containsagreaternumberofPO(70)unitsincomparisontoEO(38)unitswhichmakesP103apredominantlyhydrophobicpolymer.
Thus,intheeventofmicelleformationwithotherTBPs,P103willprefertohavemaximumsynergisticmixingwithsimilarpredominantlyhydrophobicTBPssuchasL64ratherthanP104andP123withmuchhighernumberofPOunitsincomparisontoEOwhichwillinducestericeffectsinthecore,resultingintheunfavorablemixing.
TemperatureeffectonP103+F127/P123mixturesTemperatureisanotherveryimportantparameterwhichcandrasticallyaffectthemicroenvironmentoftheTBPmicelle.
POunitsshowdramaticlossofwaterorhydrationincomparisontoEOunitsastemperatureincreases.
Inthefirstcombination,therelativedifferencebetweenthemolecularweightsofPPOblocksofP103andF127ismuchlessincomparisontothatamongPEOblocks.
Inthelattercase,thisdifferenceismoresignificantforPPOblocksratherthanthatofPEOblocks.
Hence,wewanttoseewhichcombinationofthesetwowouldpro-ducegreaternon-idealbehavior(favorableorunfavor-able)intheirmixedstateandalsoundertheeffectoftemperaturevariation.
ThemixedCMCvaluesareshowngraphicallyinFigures5and6alongwiththeidealCMCvalues.
TheexperimentalCMCvaluesfortheP103+F127mixture(Figure5)arelowerthantheidealbehaviorat25°C,andthisdifferencedecreasesasthetemperatureincreasesfrom25°Cto40°C.
Incontrast,theexperimentalvaluesarequiteclosetotheidealonesfortheP103+P123mix-ture(Figure6)at25°Cbutbecomesignificantlyhigherastemperatureincreases.
ItmeansthatP103+F127showsattractiveinteractionsat25°Cthatdecreasewiththetemperature,whileP103+P123,ontheotherhand,behavesalmostideallyat25°Cbutbecomesincreasinglynon-idealastemperaturesincreases.
SincethetemperaturevariationhasadramaticeffectonthehydrationofmixedTBPmicelles,therefore,thiseffectshouldreflectfromtheviscositymeasurements.
Plotsofexcessrelativeviscosity(Δηr)ofbothmixturesoverthewholemolefractionrange(Figure7)demonstratenegativedeviationat25°CforP103+F127thatdecreasesasthetemperatureincreases,whileat40°C,italmostfollowstheadditivityrule.
Whereas,ΔηrforP103+P123mixturesshowsacomparativelyveryweaknegativedeviationat25°Cfromanidealbe-haviorthatdecreasesandrevertstoaweakpositivedeviationastemperatureincreases.
ThenegativedeviationsinΔηrvaluesgenerallyarisefromthedecreaseinfluidityinthebulkuponmixingtwocomponents.
ThatishappeningduetoattractiveinteractionsbetweenthemicellesofP103andF127inordertoformmixedmicelleswhichenhancetheaggre-gation,andhence,agreaternumberofaggregatesre-ducefluidity.
However,whentemperatureincreases,itcausesdehydrationofPOandEOgroupswhichisrela-tivelyrapidforthePOgroupcomparedtotheEOgroupandhenceleadstoinstabilitytothemixedmicelles,That,inturn,reducestheaggregationduetothemixedmicelleformation,andhence,fluidityincreasesandapproachestheidealbehavior.
Ontheotherhand,theweaknegativedeviationinP103+P123mixturesat25°Cisagainduetoincreasedfluidity,butthatrevertstoidealbehaviorastemperatureincreasesandevenshowspositivedeviationathighertemperatures.
Itmeansthatthedehy-drationinP103andP123micelleshappenstosuchanextentthatbothcomponentsstartshowingunfavorablemixing.
Itallhappensduetothepresenceofamuchlar-gernumberofPOunitsinbothP103andP123whichdehydraterapidlyastemperatureincreasesandevenloosesolubilityintheaqueousphase.
Thisreducesthe-6-5-4-3-2-101200.
511.
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5ββββAvgPPO/PEOFigure4Plotofinteractionparameter,βAvg,versusPPO/PEOratioofthetriblockpolymers.
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81cmc(P103+F127)cmc*P103P103+F127-400Ccmc/10-4moldm-3Figure5PlotofmixedCMCversusαP103forP103+F127mixtureatvarioustemperatures.
CMC*istheidealCMCvalue.
Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12Page7of18http://www.
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com/content/4/1/12micelleformationineachcase,andhence,thesystemapproachestheidealbehaviorastemperaturestartsin-creasingbuteventuallyrevertstopositivedeviationsatahighertemperatureduetodecreasedsolubility.
Temperatureeffectcanfurtherbeevaluatedbycom-putingtheregularsolutionparameterβforeachmixtureatα1=0.
5(β0.
5)(Figure8).
Bothmixturesstartwithnegativeβvaluesat25°C,whichbecomelessnegative0.
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81cmc(P103+P123)cmc*cmc/10-4moldm-3P103P103+P123-400CFigure6PlotofmixedCMCversusαP103forP103+P123mixtureatvarioustemperatures.
CMC*istheidealCMCvalue.
Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12Page8of18http://www.
industchem.
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Thevaluesremainnegativefrom25°Cto40°CforP103+F127,whilethoseforP103+P123changetopositivesomewherecloseto30°C.
Withintheframeworkoftheregularsolutiontheory,thenegativeβvalueisexplainedonthebasisofattractiveinteractionsbetweentheunlikeTBPcompo-nents,whilethepositivevaluecanbeduetotheun-favorablemixing.
Thus,anincreaseinthetemperaturebringsunfavorablemixingamongbothunlikeTBPcomponentsinbothkindsofmixedmicelles.
AgreaterdehydrationofPOgroupsinthecaseofP103+P123mixtureswithgreaternumberofPOunitsshowsastrongertemperatureeffect,andthatiswhyβshiftstoapositivevalueatamuchlowertemperaturearound30°C.
Whereas,thisisnothappingoverthewholetemperaturerangestudiedinthecaseofP103+F127mixturesduetothepresenceofarelativelylessernum-berofPOgroups.
AlthoughmixedmicelleformationbetweentwoTBPsisgovernedbythepredominantlyhydrophobicinteractionsoperatingbetweenthepre-dominantlyhydrophobicPPOdomainsofunlikeTBPs,anincreaseinthetemperaturereducestheiraqueousphasesolubilityandadverselyaffectsthehydrophobicinteractionsresponsibleforthemixedmicelleforma-tion.
ThatiswhythiseffectismoreprominentinthecaseofP103+P123mixtureswithalargerPPOdo-mainincomparisontothatofP103+F127.
CriticalmicelletemperatureTBPsareknowntohavemicelleformationwithrespecttothevariationoftemperature,andthetemperaturewhereithappensisknownasCMT,ananalogoustermusedforthispurposetothatofCMCwheremicellefor-mationoccursduetoachangeinconcentration.
CMTisconsideredtobehavingmorerelevanceasfarastheirshelflifeundervaryingtemperaturesisconcernedbe-causemanyindustrialproductsinthecosmeticindustryconsistofmorethanoneTBPcomponent.
Although,severalstudieshavereportedtheCMT,littleisknownaboutthemixedCMTbehavior.
ExperimentalCMTvaluesforsomebinarymixturesareshownin(Figure9)alongwiththeidealmixing.
Inmostcases,theyshownegativedeviationsfromidealbehaviorexceptinthecaseofP104+P103wheretheCMTvaluesmainlylieclosetothatoftheidealbehavior.
AnegativedepartureofCMTvaluesindicatesthatthemixedmicellizationistakingplaceatlowertemperaturesandcanbeexplainedonthebasisoffavorableinteractionsbetweentheunlikeTBPcomponents,andthatshiftsthemixedCMTtolowertemperatures.
GreaterdepartureaccountsforstrongerinteractionsbetweenthecomponentsofP103+L64/P84binarymixtures.
Theclose-to-idealmixinghappeninginthecaseofP104[(EO)18(PO)58(EO)18]andP103[(EO)17(PO)60(EO)17]isduetothelittledifferencebetweenthenumberofPOaswellasEOunits.
Thisallowstheunlikepolymermacromoleculetoaccommodateinthemixedstatewithoutsignificantalterationsintheoverallhydrophilicorhydrophobicenvironment.
Onthecon-trary,thisisnotthecasewhenL64[(EO)13(PO)30(EO)13]andP84[(EO)19(PO)43(EO)19]havebeentaken.
Inboththesecases,thereisalargedifferenceinthePOunitsofthesepolymerscomparedwiththatofP103.
Thus,intheeventofmixedmicelleformation,alargerPPOblockofP103hastoaccommodatewiththe-0.
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05000.
20.
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60.
81252830323540rP103P103+P123abFigure7Plotofexcessrelativeviscosity,Δηr,versusαP103.
For(a)P103+F127and(b)P103+P123mixturesoverthewholemolefractionrangeatdifferenttemperatures.
-3-2-1012202530354045P103+F127P103+P123(0.
5)Temperature/oCFigure8Plotofregularsolutioninteractionparameter,β(0.
5),versustemperature.
ForP103+F127andP103+P123mixturesatαP103=0.
5.
Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12Page9of18http://www.
industchem.
com/content/4/1/1220253035404500.
20.
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81cmtexc(P103+L64)cmt(P103+L64)cmt*cmtexc,cmt(oC)P10320253035404500.
20.
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60.
81cmtexc(P104+P84)cmt(P104+P84)cmt*cmtexc,cmt(oC)P10420253035404500.
20.
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81cmtexc(P104+P84)cmt(P104+P84)cmt*cmtexc,cmt(oC)P10420253035404500.
20.
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81cmtexc(P104+P103)cmt(P104+P103)cmt*cmtexc,cmt(oC)P10420253035404500.
20.
40.
60.
81cmtexc(L64+P84)cmt(L64+P84)cmt*cmtexc,cmt(oC)L6420253035404500.
20.
40.
60.
81cmtexc(L64+P104)cmt(L64+P104)cmt*cmtexc,cmt(oC)L64Figure9PlotofCMTandCMTexc(°C)versusαP103,P104,L64.
ForP103+L64,P103+P84,P104+P103,P104+P84,L64+P104,andL64+P84binarymixtures.
Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12Page10of18http://www.
industchem.
com/content/4/1/12shorterPPOblockofeitherL64orL84inthecoreofthemixedmicelle.
Thisensuresthemicelletransitionswithgreatercompatibilityamongthecomponentsinthemixedstate(Figure9).
Quenchingofpyrenebyasuitablequencher(Q)suchashexadecylpyridiniumchloride(HPyCl)understeady-stateconditionscanalsobeusedtoexplaintheseresultsandassumedthatthefluorescencelifetimeofpyreneislongerthantheresidencetimeofthequencherinamicelle.
Asuitable[pyrene]/[mixedmicelle]and[Q]/[mixedmicelle]ratiosensurethePoissondistribution.
Thefluorescenceintensityofthefirstvibronicbandof(Figure10)pyrenedecreaseswiththeincreasein[Q]withouttheappearanceofanynewband(notshown).
AStern-Volmerrelation-shipisusedtocalculatethecollisionalquenchingcon-stant,calledtheStern-Volmerconstant(KSV)[99-102].
TheseKSVvaluesforvariousbinarymixtures(Figure11)varynonlinearlywithpositivedeviationsfromtheideality,whicharepredominantinthecaseofP103+L64/P84,thusdemonstratingthatthequenchingisfacilitatedinthesemixtures.
Thiscanbeattributedtothepresenceofasuitablesolubilizingenvironmentprovidedbythemixedmicellesforaneffectivequenchingtotakeplace.
ThequenchingisprominentintheL64/P84-richregionofthemixturewhichmeansthatthesmallamountoftheinductionofP103generatesafavorableenvironmentforthesolubilizationofboththequencherandpyrene.
IntherichregionofP103,themuchlargermicellarcorewithpredominantlygreateramountofPOunitswillmaketheencountersofboththequencherandpyrenedifficult;asaresult,quenchingdecreases.
Theexcimeremissionisproducedbythecollisionalquenchingbetweentheexcited(Py*)andgroundstate(Py)monomersofthefluorescenceprobe.
Thus,the02040608010000.
20.
40.
60.
81L64+P104L64+P84KSVx10-3/mol-1dm-3L6410152025303540455000.
20.
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81P103+L64P103+P84KSVx10-3/mol-1dm-3P10310152025303540455000.
20.
40.
60.
81P104+P103P104+P84KSVx10-3/mol-1dm-3P104Figure11PlotofKSVversusαP103/P104/L64.
ForP103+L64/P84binarymixtures,P104+P103/P84binarymixtures,andL64+P104/P84binarymixturesat45°C.
Figure10Pyreneemissionspectrumatvarioustemperaturesof[P103]=5.
0*104moldm3.
I1,I3,andIexcaretheintensitiesofthefirst,third,andexcimerbandsofpyrene.
Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12Page11of18http://www.
industchem.
com/content/4/1/12mechanismoftheexcimerdimer(D*)formationcanbewritteninthefollowingway:PyPykEFkEDD1Py→kMFPyhv2D→kDF2Pyhv;3wherekEF,kED,kMF,andkDFaretheconstantsofexcimerformation,excimerdissociation,monomerfluorescence,anddimerfluorescence,respectively.
Thekineticsofexcimerformationcanfurtherbeexplainedundertwosetsofexperimentalconditions,i.
e.
,low-temperatureandhigh-temperaturebehaviorswithinthetemperaturerangestudiedherein.
Atlowtemperature,Iexc/I1ratiocanbewrittenas:IeI1k1EFPykMFexpWEF=kT;4wherek1EFandWEFarethefrequencyfactor(limitingvalueofk1EFasT∞)andactivationenergyofexcimerformation,respectively,andkisBoltzmann'sconstant.
Similarly,athightemperature,theIexc/I1ratioisgivenby:IeI1kDFk1EFPyk1EDkMFexpBkT=;5whereBistheexcimerbindingenergy=WEDWEF,andk1EFisthefrequencyfactor.
Equations4and5suggestthatln(Iexc/I1)showsanincreaseanddecreaselinearlywith1/T,respectively,atfixed[Py].
Figure12showssuchavariationforP104atdifferenttemperatures.
Here,anintersectionoftwolinearlinesgivestheCMT26°C.
Hence,thekineticsofpyrenesolubilizationinTBPmicellescanbeanalyzedwithintwodifferentsetsofexperimentalconditions,oneisbelowandtheotherabove26°C.
Theformergivestheactivationenergyfortheexcimerformation(Figure13),whilethelattergivesthebindingenergy(Figure14)betweenPy*andPy.
Figure13showsthevariationofWEFoverthewholemolefractionrangeforallmixtures.
ThesevaluesforP103+L64/P84(Figure13,top)showapositivedevi-ationfromtheidealmixing(shownbydottedlines),-50-40-30-20-10000.
20.
40.
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81P103+P84P103+L64WEF/kJmol-1P103-50-40-30-20-10000.
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81P104+P103P104+P84WEF/kJmol-1P104-50-40-30-20-10000.
20.
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81L64+P104L64+P84WEF/kJmol-1L64Figure13Plotofenergyofactivation(WEF)ofthepyreneprobefortheexcimerformationversusαP103/P104/L64.
ForP103+L64/P84binarymixtures,P104+P103/P84binarymixture,andL64+P104/P84binarymixtures.
-2.
2-2-1.
8-1.
6-1.
4-1.
2-13.
253.
33.
353.
43.
453.
5ln(Iexc/I1)1/T103Figure12Plotofln(Iexc/I1)versus1/TforpureP104at[P104]=5.
0*104moldm3.
Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12Page12of18http://www.
industchem.
com/content/4/1/12whilethoseforP104+P103/P84(Figure13,middle)re-mainmostlyclosetotheidealbehavior.
Figure13(bot-tom)showsnegativedeviationsinWEFvaluesfromidealityforL64+P104/P84mixtures.
AdecreaseintheWEFvaluesatallmolefractionsofP103+L64/P84canbeattributedtothefacilitationoftheexcimerformationwhichisalsoevidentfromthehigherKSVvaluesforthesemixtures.
Theseresultscanalsoberelatedtotherelativeviscosity(ηr)behaviorforthesemixtures(Figure15).
AsmallerηrvaluethantheidealbehaviorespeciallyintheP103-poorregionofthemixturesshowstheattractiveinteractionsbetweenthecomponentsthatmightberesponsibleforlowerWEFincomparisontotheirpurestates.
Thisisfurthersupportedbythenegative11.
051.
11.
151.
200.
20.
40.
60.
81P103+L64P103+P84rP1031.
0141.
0151.
0161.
0171.
0181.
0191.
0200.
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40.
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81L64+P104L64+P84rL6411.
021.
041.
061.
081.
11.
121.
1400.
20.
40.
60.
81P104+P103P104+P84rP104Figure15PlotofηrversusαP103/P104/L64.
ForP103+L64/P84binarymixtures,P104+P103/P84binarymixtures,andL64+P104/P84binarymixturesat45°C.
0102030405000.
20.
40.
60.
81P103+P84P103+L64B/kJmol-1P1030102030405000.
20.
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81P104+P103P104+P84B/kJmol-1P1040102030405000.
20.
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81L64+P84L64+P104B/kJmol-1L64Figure14Plotofbindingenergy(B)ofthepyreneprobefortheexcimerformationversusαP103/P104/L64.
ForP103+L64/P84binarymixtures,P104+P103/P84binarymixture,andL64+P104/P84binarymixtures.
Singhetal.
InternationalJournalofIndustrialChemistry2013,4:12Page13of18http://www.
industchem.
com/content/4/1/12deviationsinBvaluesfromtheidealbehavior(Figure14,top).
ThevariationintheBvaluesforthesemixtures(Figure14,middle)fullysupportsthisfact.
TheηrofP104+P84mixtures(Figure15,middle)showsclearidealmixing,butthenegativedeviationinthecaseofP104+P103isduetounknownreasons.
AnincreaseintheWEFvalueforL64+P103/P84mixtures(Figure13,bottom)fromtheirpurecomponentsclearlyindicatesthereductioninexcimerformation.
ThisisagaincomplimentarywiththepositivedeviationsintheBvaluesfromthecorrespondingidealmixing(Figure14,bottom).
BothfiguresdemonstratethatthevariationinWEFandBvaluesismainlypredominantintheL64-poorregionsofbothmixtures.
Thepositivedeviationsintheηr(Figure15,bottom)fromtheidealbehaviorespeciallyintheL64-poorregionfurtherconfirmtheseresults.
Thevariationofallthemicellarparametersandphoto-physicalpropertiesindicatesthatthemixedmicellesbetweenthecomponentsofP103+L64andP103+P84mixturesformduetoattractiveinteractions.
Theseinter-actionsarisefromthemutualcompatiblearrangementamongtheunlikeTBPmonomersinthemixedstateinsuchawaythatsterichindrancesareminimized.
Ontheotherhand,mixturesofP104+P103andP104+P84prefertoremainidealintheirmixedstate,whilethemixturesofL64+P104andL64+P84showmainlyunfavorablemixing.
ApplicationsSolubilizationanddrugdeliveryagentsThelowsolubilityinbiologicalfluidsdisplayedbyabout50%ofthedrugsstillremainsthemainlimitationinoral,parenteral,andtransdermaladministration.
Toovercomethesedrawbacks,inclusionofhydrophobicdrugsintopolymericmicellesisoneofthemostattractivealterna-tives.
Amphiphilicpoly(ethyleneoxide)-poly(propyleneoxide)blockcopolymersarethermoresponsivematerialsthatdisplayuniqueaggregationpropertiesinaqueousmedium.
Duetotheirabilitytoformstablemicellarsys-temsinwater,thesematerialsarebroadlystudiedashydrosolubilizersforpoorlywater-solubledrugs.
Thisoccursbecausethecoreofthemicelleprovidesahydro-phobicmicroenvironment,suitableforsolubilizingsuchmolecules.
Thephenomenonofsolubilizationformsthebasisformanypracticalapplicationsofamphiphiles.
ThemostimportantapplicationsofPEO-PPO-basedcopolymersinthepharmaceuticaltechnologyfieldareforattainingimprovedsolubility,stability,release,andbioavailabilityofdrugs[103].
HydrophobicPluronicblockcopolymers(PBC)formlamellaraggregateswithahighersolubilizationcapacitythansphericalmicellesformedbyhydrophilicPBC.
However,theyalsohavealargersizeandlowstability.
Toovercometheselimita-tions,Kabanovetal.
[104]preparedbinarymixturesfromhydrophobicPBC(L121,L101,L81,andL61)andhydrophilicPBC(F127,P105,F87,P85,andF68).
Inmostcases,PBCmixtureswerenotstable,revealingfor-mationoflargeaggregatesandphaseseparationwithin1to2days.
However,stableaqueousdispersionsoftheparticleswereobtainedupon(1)sonicationofthePBCmixturesfor1or2minor(2)heatingat70°Cfor30min.
Itwasobservedthatamongallcombina-tions,L121/F127mixtures(1:1%weightratio)formedstabledispersionswithasmallparticlesize.
Thesolu-bilizingcapacityofthissystemwasexaminedusingamodelwater-insolubledye,Sudan(III).
MixedL121/F127aggregatesexhibitedapproximatelytenfoldhighersolubi-lizationcapacitycomparedtothatofF127micelles.
Thus,stableaqueousdispersionsofnanoscalesizewerepreparedfrommixturesofhydrophobicandhydrophilicPBCbyusingtheexternalinputofenergy.
Thepreparedmixedaggregatescanefficientlyincorporatehydrophobiccom-pounds.
Toenhancestabilityofmicellesinthebloodstreamupondilution,PluronicL121micelleswerecross-linkedthroughtheirhydrophilicshells[105].
Toformthecross-links,theendhydroxylgroupsofPluronicL121werefirstchemicallyconvertedtoaldehydesandthenbridgedviaSchiffbases.
ThisgreatlyreducedtheCMCofthemicellesandenhancedthemicellestability.
AseriesofstudiesusedPluronicP105micellesforthedeliveryofDoxintosolidtumorsinmice[106-109].
Inthesestud-ies,thelocalizedultrasonicirradiationofthetumorwasapplieduponaccumulationofthemicellesinthetumorinterstitiumtofacilitatethedrugreleaseintothetumorcells[108].
Furthermore,theultrasound-enhancedintracellularuptakeofDoxadministeredwiththePluronicP105micelleswasdemonstratedinvitro[106].
ItwassuggestedthattheenhanceduptakewascausedbyeithermicelledisintegrationthatreleasedfreeDoxorcellmembraneperturbationsthatfacilitatedthecellularuptakeofthemicellesasawhole.
Overall,micellardeliverycombinedwithultrasonicirradiationresultedinasubstantialdecreaseofthetumorgrowthratescomparedtoapositivecontrol.
NanodrugdeliveryPolymernanomaterialshavesparkedaconsiderableinterestasvehiclesusedfordiagnosticandtherapeuticagents;researchinnanomedicinehasnotonlybecomeafrontiermovementbutisalsoarevolutionizingdrugdeliveryfield.
Acommonapproachforbuildingadrugdeliverysystemistoincorporatethedrugwithinthenanocarrierthatresultsinincreasedsolubility,metabolicstability,andimprovedcirculationtime.
Therecentdevel-opmentsindicatethatselectpolymernanomaterialscanimplementmorethanonlyinertcarrierfunctionsbybeingbiologicalresponsemodifiers.
ThePluronicblockcopoly-merscausevariousfunctionalalterationsincells.
ThekeySinghetal.
InternationalJournalofIndustrialChemistry2013,4:12Page14of18http://www.
industchem.
com/content/4/1/12attributeforthebiologicalactivityofPluronicsistheirabilitytoincorporateintomembranesfollowedbysubse-quenttranslocationintothecellsandaffectingvariouscellularfunctions,suchasmitochondrialrespiration,ATPsynthesis,activityofdrugeffluxtransporters,apoptoticsignaltransduction,andgeneexpression.
Asaresult,PluronicscausedrasticsensitizationofMDRtumorstovariousanticanceragents,enhancedrugtransportacrosstheblood-brainandintestinalbarriers,andcausetran-scriptionalactivationofgeneexpressionbothinvitroandinvivo.
Pluronicshaveabroadspectrumofbiologicalresponse-modifyingactivitieswhichmakeitoneofthemostpotentdrugtargetingsystemsavailable,resultinginaremarkableimpactontheemergentfieldofnanomedi-cine.
IncorporationoflowmolecularmassdrugsintoPluronicmicellescanincreasedrugsolubilityanddrugstabilityandcanimprovedrugpharmacokineticsandbio-distribution.
PolymericmicelleswereutilizedfordeliveryofCNSdrugsacrosstheblood-brainbarrier[110,111],oraldeliveryofdrugs[112-114],andtumor-specificdeliv-eryofantineoplasticagents[115-117].
Forexample,neuro-lepticdrug-loadedPluronicP85micellesweretargetedtothebrainbyconjugatingthemicelleswithneurospecificantibodiesorinsulinastargetingmoieties[118].
Anim-provementoforalbioavailabilityofapoorlywater-solublephytoestrogen,genistein,wasachievedbyincorporationofthisdrugintoPluronicF127micelles[117].
Pluronicblockcopolymerswerealsoreportedtosignificantlyenhancethebioavailabilityofvariousantibacterialandantifungaldrugsandtoenhancetheactivityofthesedrugswithrespecttomanymicroorganisms[119-122].
Leeetal.
[123]developedabinarymixingsystemwithtwoPluronics,L121/P123,asananosizeddrugdeliverycarrier.
Thelamellar-formingPluronicL121(0.
1wt.
%)wasincorporatedwithPluronicP123toproducenanosizeddispersions(inthecaseof0.
1and0.
5wt.
%P123)withhighstabilityduetoPluronicP123andhighsolubilizationcapacityduetoPluronicL121.
Thebinarysystemsweresphericalandlessthan200nmindiameter,withhighthermodynamicstability(atleast2weeks)inaqueoussolution.
TheCMCofthebinarysys-temwaslocatedinthemiddleoftheCMCofeachpoly-mer.
Inparticular,thesolubilizationcapacityofthebinarysystem(0.
1/0.
1wt.
%)washigherthanmono-systemsofP123.
Themainadvantageofbinarysystemsisovercominglimitationsofmono-systemstoallowtailoredmixingofblockcopolymerswithdifferentphysicochemicalcharac-teristics.
Kadametal.
[124]investigatedtheeffectofthemolecularcharacteristicsofEO-POtriblockcopolymersPluronicP103(EO17PO60PEO17),P123(EO19PO69EO19),andF127(EO100PO65EO100)onmicellarbehaviorandsolubilizationofadiureticdrug,hydrochlorothiazide(HCT).
TheCMTsandsizeforemptyaswellasdrug-loadedmicellesarereported.
TheCMTsandmicellesizedependedonthehydrophobicityandmolecularweightofthecopolymer;adecreaseinCMTandincreaseinsizewereobservedonsolubilization.
ThesolubilizationofthedrugHCTintheblockcopolymernanoaggregatesatdifferenttemperatures(28°C,37°C,45°C)andpH(3.
7,5.
0,6.
7)andinthepresenceofaddedsalt(NaCl)wasmonitoredbyusingUV-visspectroscopy,andsolu-bilitydatawereusedtocalculatethesolubilizationchar-acteristics:micelle-waterpartitioncoefficient(P)andthermodynamicparametersofsolubilizationviz.
Gibbsfreeenergy(ΔGs°),enthalpy(ΔHs°),andentropy(ΔSs°).
Itisobservedthatthesolubilityofthedrugintheco-polymerincreaseswiththetrend:P103>P123>F127.
Thesolubilizeddrugdecreasedthecloudpoint(CP)ofcopolymers.
ResultsshowedthatthedrugsolubilityincreasesinthepresenceofsaltbutsignificantlyenhanceswiththeincreaseinthetemperatureandatalowerpHinwhichthedrugremainsinthenonionizedform.
SynthesisofgoldnanoparticlesGoldnanoparticlesareagreatdealofrecentinterestinthecontextofemergingnanotechnologyapplications.
Atthenanoscale,theyexhibituniquequantumandsurfaceproperties,differentfromthoseofatomsaswellasbulkmaterials[125-128].
Dependingontheapplicationstheyarebeingsynthesizedfor,theycanbesynthesizedinmanydifferentways.
Oneoftheeasiestandconvenientwaysisthechemicalreductionmethodwhichinvolvestheuseoffourbasicmaterials,namely,solvent,metalsalt,reducingagent,andstabilizingagent[129-131].
Re-cently,theuseofblockcopolymersforthesynthesisofgoldnanoparticlesisfoundtohavemanyadvantages;forexample,ablockcopolymernotonlyplaysthedualroleofreductantandstabilizerbutalsoprovidesaneconom-icalandenvironmentallybenignwayforthesynthesisofgoldnanoparticles[132-134].
Thehydrophobicblocksoftheblockcopolymers(PPO)formthecoreofthesemicellaraggregates,whereasthehydrophilicones(PEO),withthesurroundingwatermolecules,formthecorona.
Theblockcopolymerscanbeusedtoproducemetalnanoparticlesbecauseoftheirabilitytoreducemetalions.
Onmixingtheaqueoussolutionofmetal(e.
g.
,gold)saltandblockcopolymers,thesepolymericnanostructuredmatrixesengulftheionicmetalprecursors,whichaftersubsequentreductionformnanoparticles.
Self-assemblyofablockcopolymerinthismethodisutilizedtocontrolthesynthesisofgoldnanoparticles[135].
TheformationofgoldnanoparticlesfromAuCl4comprisesthreemainsteps:reductionofAuCl4ionsbytheblockcopolymersinthesolutionandformationofgoldclusters,adsorptionofblockcopolymersongoldclustersandreductionofAuCl4ionsonthesurfacesofthesegoldclusters,andgrowthofgoldparticlesinstepsandfinallyitsstabilizationbyblockcopolymers[136].
Theroleofblockcopolymersinthesynthesis(formationrate,yield,stability,shape,andsizeofSinghetal.
InternationalJournalofIndustrialChemistry2013,4:12Page15of18http://www.
industchem.
com/content/4/1/12nanoparticles)varieswiththeirmolecularweight,PEO/PPOblocklength,polymerconcentration,andtemperature[137-139].
Theformationofhigh-concentrationgoldnano-particlesatroomtemperatureisreportedintheblockcopolymer-mediatedsynthesiswherethenanoparticleshavebeensynthesizedfromhydrogentetrachloroaureate(III)hydrate(HAuCl4.
3H2O)usingblockcopolymerP85(EO26PO39EO26)inaqueoussolution[140].
Theformationofgoldnanoparticlesinthesesystemshasbeencharacter-izedusingUV-visiblespectroscopyandSANS.
Itshowedthatthepresenceofanadditionalreductant(trisodiumcit-rate)canenhancenanoparticleconcentrationbymanyfold,whichdoesnotworkintheabsenceofeitherofthese(add-itionalreductantandblockcopolymer).
Bakshietal.
[141]usedaqueousmicellarsolutionsofF68(PEO78-PPO30-PEO78)andP103(PEO17-PPO60-PEO17)triblockpolymerstosynthesizegold(Au)nanoparticlesatdifferenttempera-tures.
TheyobservedthatallreactionswerecarriedoutwiththePEO-PPO-PEOmicellarsurfacecavitiespresentatthemicelle-solutioninterfaceandwerepreciselycon-trolledbythemicellarassemblies.
MarkeddifferencesweredetectedwhenpredominantlyhydrophilicF68andhydrophobicP103micelleswereemployedtoconductthereactions,andthepresenceofwell-definedpredominantlyhydrophobicmicelleswithacompactmicelle-solutioninterfacialarrangementofsurfacecavitiesultimatelycon-trolledthereaction.
MesomorphousbehaviorNumerousinvestigationsofthebehaviorofPEO-PPO-PEOtriblockcopolymersinaqueoussolutionsandtheadsorp-tionofthesecopolymersatsolid-liquidinterfaceswerecarriedoutinthepastdecades[31,52,142].
Also,sincetheaggregatedstructureofPEO-PPO-PEOtriblockcopoly-mersiscontrolleddependingontemperature,concen-tration,andtheadditionofadditives,theyhavebeenusedasstructure-directingorganicmaterialsforthesynthesisofinorganicmaterialswithacontrolledsize,shapeandstructure.
Bagshawetal.
preparedmesopor-oussilicamolecularsievesusingnonionicpolyethyleneoxidesurfactantsinaneutralcondition[143].
Thehydrogenbondingbetweenthehydrophilicpartofpoly-mersandtheinorganicprecursorfollowedbymolecularrearrangementinvolvingtheamphiphilicnatureofpolymerswasthekeyfactorforthepreparationofthismaterial.
Zhaoetal.
reportedonthesynthesisofmeso-poroussilicastructuresusingnonionicalkylpoly(oxy-ethylene)surfactantsandpoly(alkyleneoxide)blockcopolymersinanacidmedia,whichincludedcubic,three-dimensionalhexagonal,two-dimensionalhexagonal,andlamellarmesostructures[144].
Kimetal.
developedaneconomicalandsimplemethodforthepreparationofsub-micrometerhematiteparticleswithanarrowsizedistributionandanisotropicshape.
Toobtainhematiteparticles,theferricionsolutionwasagedatanelevatedtemperatureinthepresenceofpoly(ethyleneoxide)-block-poly(propyleneoxide)-block-poly(ethyleneoxide)(PEO-PPO-PEO)triblockcopolymerEO20PO70EO20(P123).
Theresultingparticlesalsoshowadisorderedmesoporousstructureandretaintheirshapeaftercalcina-tions[145].
Huangetal.
synthesizedaseriesofhighlyorderedmesoporouscarbonaceousframeworkswithdi-versesymmetriesbyusingphenolicresolsasacarbonprecursorandmixedamphiphilicsurfactantsofpoly(ethyleneoxide)-b-poly(propyleneoxide)-b-poly(ethyleneoxide)(PEO-PPO-PEO)andreversePPO-PEO-PPOastemplatesbythestrategyofevaporation-inducedorganic-organicself-assembly[146].
Theblendsofblockcopoly-merscaninteractwithresolprecursorsandtendtoself-assembleintocross-linkingmicellarstructuresduringthesolventevaporationprocess,whichprovidesasuit-abletemplatefortheconstructionofmesostructures.
Anunderstandingoftheorganic-organicself-assemblybehaviorinthemixedamphiphilicsurfactantsystemwouldpavethewayforthesynthesisofmesoporousmaterialswithcontrollablestructures.
OtherapplicationsCobaltdeterminationdaSilvaetal.
[147]proposedanewmethodforCo(II)determinationbasedontheuseofthetriblockcopolymerasmicellarmediuminsteadofchloroform.
Theproposedstrategyisenvironmentalfriendlybecausethecopolymerisbiodegradableandnontoxic.
Themethodisbasedontheformationofacobalt-1-nitroso-2-naphtholcomplexinthemicellartriblockcopolymercompoundsolutionconstitutedbyPEOandPPO.
ExperimentalconditionssuchaspH,themolecularweight,andthePEO/PPOratioofthetriblockcopolymerwereoptimized.
Resultsobtainedforcobaltdeterminationinvitaminswiththisnovelmethodshowedexcellentagreementwiththoseobtainedusingatomicabsorptionspectrometry.
BoundarylubricationLubricantsmostcommonlyusedintextilemanufacturingarecomposedoffattyacids,mineraloils,ethoxylatedacids,andsilicones.
Poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene)(PEO-PPO-PEO;Pluronic)triblockcopoly-mershavebeenofgreatinterestaslubricantsduetotheirnumerousadvantages,includinggoodsolubilityinwaterandorganicsolvents,compatibilitywithmostsurfactants,andavailabilityaselectrolyte-freematerial.
ThemolecularweightandthePEO/PPOratioofthesesurfactantscanbeadjustedtotailortheirpropertiesaslubricants,texturizers,softeners,emulsifiers,dispersers,andantistaticandwettingagents.
Pluroniccopolymershavehighwettingandspreadingability,allowingthemtoformuniformcoatingsontextilesthatcanresultinSinghetal.
InternationalJournalofIndustrialChemistry2013,4:12Page16of18http://www.
industchem.
com/content/4/1/12lowfriction,antistaticproperties,dye-levelingimprove-ment,andeasycleaning.
Lietal.
[148]studiedlubrica-tionbehaviorofanaqueoussolutionofPEO-PPO-PEOsymmetrictriblockcopolymeronthinfilmsofpolypro-pylene(PP),polyethylene(PE),andcellulose.
ItwasobservedthatthefrictioncoefficientonPPandPEwasreducedafteradsorptionfromthePEO-PPO-PEOaque-oussolution,whiletheoppositeeffectwasobservedforcellulosesurfaces.
XPSwasusedtoverifythepresenceofthelubricantonthepolymericsubstratesandtoevaluateitsremovalbywaterwashing.
ThelubricantlayerwaseasilyremovedwithwaterfromthePPandcellulosesurfaces,whileadurablelayerwasfoundonPE.
Asmembranematerialforintermediate-temperatureDMFCsTriblockcopolymer/Nafionblendmembranes(DuPont,Wilmington,DE,USA)facilitateprotonconductionindir-ectmethanolfuelcells(DMFCs)atintermediatetempera-tures.
Huetal.
[149]investigatedtheinteractionbetweenthetwopolymercomponentsbyFT-IRspectroscopy.
TheblendmembranesshowhigherprotonconductivitythanrecastNafionunderpartiallyanhydrousconditions.
Pro-tonscanbetransportedwiththeassistanceofanetherchainundersuchconditionsatelevatedtemperature.
Inaddition,themembranesexhibitmorefavorablemethanolpermeabilityandselectivity.
ThiskindofblendmembraneshowssomewhatbetterperformanceinDMFCcom-paredtobarerecastNafionatintermediatetemperature(≥120°C).
Thishelpstodesignmembranematerialswithenhancedprotonconductivityunderconditionstypicalofintermediate-temperatureDMFCs.
ConclusionsMixedmicelleparametersofdifferentTBPsmixturesarediscussed.
IthasbeenobservedthatsynergisticmixingisgovernedbythecompatibilitybetweenthedifferentblocksofPEOunitsofdifferentTBPs.
AlargedifferencebetweenthePPOandPEOblocksofdifferentpolymersleadstotheunfavorablemixing.
ThesefindingshelpustofurtherexploretheindustrialapplicationsofsuchTBPs.
CompetinginterestsTheauthorsdeclarethattheyhavenocompetinginterests.
Authors'contributionsVScollectedthereferencesforthisworkanddidadditionalstudiesandcalculations.
PartofthisworkisrelatedtothePh.
D.
thesisofNK.
PKcompiledandwrotethereviewalongwithPND.
Allauthorsreadandapprovedthefinalmanuscript.
AcknowledgmentsPKacknowledgesthefinancialassistancefromtheDST(Ref#SERB/F/0328/2012-13)project.
Authordetails1DepartmentofChemistry,KSKVKachchhUniversity,Bhuj,Gujarat370001,India.
2DepartmentofChemistry,B.
B.
K.
D.
A.
V.
CollegeforWomen,Amritsar,Punjab143005,India.
3DepartmentofChemistry,LyallpurKhalsaCollege,Jallandhar,(Punjab)144001,India.
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